On 06/13/2009 05:09 PM, Vu Pham wrote:
Using top and ps, reports of schedule priority of tasks are different.
For example, under my two servers RHEL5.3, init has PRI of 24 under ps,
and 15 under top, events/0 has PRI of 29 under ps, and 10 under top.
Anybody experiences this problem ?
(Both servers have the lastest kernel 2.6.18-128.1.10, one 32 bits and
one 64 bits )
I asked for help from RHN for the above question and found the answer
interesting. I hope you find same thing.
---------------------------------------
| Case Information |
---------------------------------------
Case Title : [SEG]: conflict in report of scheduling priority of
proceccess
Case Number : 1927400
Case Open Date : 13-JUN-2009
Problem Type :
Last Update Comment as of 24-JUN-2009 02:32:03 :
Dear Sir,
There is some discrepancy in ps output caused by the fact that each
system may use different values to represent the process priority and
that the values have changed with the introduction of RT priorities.
The kernel stores the priority value in /proc/<pid>/stat (let's call it
p->prio) and ps reads the value and displays it in various ways to the user:
$ ps -A -o pri,opri,intpri,priority,pri_foo,pri_bar,pri_baz,pri_api,pid,comm
PRI PRI PRI PRI FOO BAR BAZ API PID COMMAND
19 80 80 20 0 21 120 -21 1 init
24 75 75 15 -5 16 115 -16 2 kthreadd
139 -40 -40 -100 -120 -99 0 99 3 migration/0
24 75 75 15 -5 16 115 -16 4 ksoftirqd/0
139 -40 -40 -100 -120 -99 0 99 5 watchdog/0
139 -40 -40 -100 -120 -99 0 99 6 migration/1
24 75 75 15 -5 16 115 -16 7 ksoftirqd/1
139 -40 -40 -100 -120 -99 0 99 8 watchdog/1
24 75 75 15 -5 16 115 -16 9 events/0
Yes, there are 8 undocumented values for the process priority that can
be passed to -o option:
Option Computed as
prioirity p->prio
intpri 60 + p->prio
opri 60 + p->prio
pri_foo p->prio - 20
pri_bar p->prio + 1
pri_baz p->prio + 100
pri 39 - p->priority
pri_api -1 - p->priority
They were introduced to fit the values in certain intervals and
compatibility with POSIX and other systems.
The top utility shows the same value as ps with "-o priority", whereas
ps with -l option shows the same value as with "-o intpri" (or "-o
opri") and if both the -l and -c options were used, ps uses the value as
with "-o pri".
Please let me know whether this answers the question.
Regards.
Nitin
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